Method of forming salicide

ABSTRACT

A method of forming a salicide. A metal layer is formed on a silicon-based substrate comprising a gate with a spacer on the side wall of the gate and a source/drain is provided. Next, a first thermal treatment is performed to make the portions of the metal layer react with the silicon in the gate and the source/drain to form a salicide. Then, any unreacted metal and the spacer are removed. An ion containing silicon is introduced into the source/drain. Finally, a second thermal treatment is performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to semiconductor manufacturing,and particularly to a method of forming a salicide without consuming thesilicon in the substrate such that junction leakage occurs.

2. Description of the Related Art

In semiconductor technology, a Metal-Oxide-Semiconductor transistorcomprises a gate and a source/drain. The gate comprising a metal layerand SiO₂ is deposited on a silicon-based substrate. Most of the metalhas bad adhesion with SiO₂. Thus, polysilicon with good adhesion isproposed to replace the metal layer. However, the resistance ofpolysilicon interconnections is so high that polysilicon is notappropriate as a conductive layer. One way to solve this problem is toform a metal salicide on the polysilicon to enhance the conductivity. Asmethods of fabricating semiconductor integrated circuits (IC)continually improve, the number of devices that may be introduced into asingle semiconductor chip has increased, while the size of each devicehas decreased. Millions of devices may now be fabricated on a singlechip. Therefore, the salicide process is widely applied to ensureshallow junction or ultra shallow junction.

FIGS. 1A-1F are schematic cross-section illustrating steps for forming asalicide of the prior art. In FIG. 1A, a substrate 10 comprises a gateoxide layer 11, a polysilicon gate 12, a source/drain 14, a spacer 20,and a field oxide 22. The substrate 10 is cleaned by HF solution, and ametal layer 30 is formed on the substrate 10 to cover the polysilicongate 12, the source/drain 14, and the spacer 20, as shown in FIG. 1B. Afirst rapid thermal process is performed at 650-700° C. in nitrogenatmosphere, and the metal salicide 31 is formed by reacting the portionsof the metal in the metal layer 30 with the silicon in the gate 12 aswell as in the source/drain 14, as shown in FIG. 1C. The portions of themetal in the metal layer 30 on the spacer 20 and the field oxide 22remain the same without reacting. Then, a second thermal process isperformed at about 800° C. in nitrogen atmosphere, and the phase of themetal salicide 31 is changed to a phase with lower resistance, as shownin FIG. 1E. The salicide process of prior art is accomplished.

The silicon in the source/drain 14 consumes the metal salicide 31 duringthe salicide process. For example, the reaction follows the followingrule when a cobalt salicide is formed: Co+Si→CoSi₂ The ratio of thethickness of Co:Si:CoSi₂ is 1:3.6:3.5. Silicon with about 360 Åthickness must be consumed to form a CoSi₂ with about 350 Å thickness.Therefore, 0.04 of the source/drain 14 is lost, and the problem of thejunction leakage following occurs, as shown in FIG. 2.

SUMMARY OF THE INVENTION

To solve above problem, it is an object of the present invention toprovide a method of forming a salicide to excess consumption of siliconin the substrate.

The method comprises the following steps. First, a silicon-basedsubstrate comprising a gate with a spacer on the side wall of the gateand a source/drain is provided. Next, a metal layer is formed accordingto the topography of the substrate to cover the gate, the spacer, andthe source/drain. A first thermal treatment is performed to react theportions of the metal in the metal layer with the silicon in the gateand the source/drain to form a salicide. Then, the unreacted metal andthe spacer are removed. An ion containing silicon is introduced into thesource/drain as an extra silicon source for salicide. Finally, a secondthermal treatment is performed.

In the preferred embodiment of the present invention, the silicon ion isintroduced by ion implantation. The first and second thermal treatmentare perferably performed by rapid thermal processes between about 600°C. and 800° C. Besides, the unreacted metal layer and the spacer areremoved by etching as is well known.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become apparent from the following detailed descriptionof preferred embodiments of the invention explained with reference tothe accompanying drawings, in which:

FIGS. 1A-1E are schematic cross-section illustrating steps for forming asalicide according to the prior art.

FIG. 2 is a schematic drawing illustrating the junction leakage problemin salicide process according to the prior art.

FIGS. 3A-3F are schematic cross-sections illustrating steps for forminga shallow trench according to the preferred embodiment of the invention.

FIG. 4 is a schematic flow chart for forming a shallow trench accordingto the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

There will now be described an embodiment of this invention withreference to the accompanying drawings, FIGS. 3A-3F and FIG. 4.

First, in step S600, a silicon-based substrate 100 with primary elementsof a MOS transistor is provided, as shown in FIG. 3A. The MOS transistorcomprises a gate 120, a source/drain 140 formed by doping, and a fieldoxide 220 on the silicon-based substrate 100, wherein the material ofthe gate 120 comprises a polysilicon. There is a spacer 200 on the sidewall of the gate 120.

Next, in the step S602, a metal layer 300 is formed according to thetopography of the MOS transistor by sputtering to cover the gate 120,the spacer 200, the source/drain 140, and the field oxide 220, as shownin FIG. 3B. The sputter process is preformed by DC plasma. The materialof the metal layer 300 comprises a transitional metal, such as titanium(Ti), cobalt (Co), nickel (Ni), or platinum (Pt).

In step S604, a first thermal treatment is preferably performed betweenabout 600° C. and 800° C. by rapid thermal process to make the portionsof the metal in the metal layer 300 react with the silicon in the gate120 and the source/drain 140 to form a salicide, as shown in FIG. 3C.However, the portions of the metal in the metal layer 300 cover thefield oxide 220 and the spacer 200 does not react with the silicon inthe substrate 100.

In step S606, any unreacted metal and the spacer 200 are preferablyremoved by conventional etching, such as wet etching, as shown in FIG.3D.

In step S608, an ion containing silicon is introduced into thesource/drain 140 by ion implantation as an extra silicon source forsalicide, as shown in FIG. 3E.

In step S610, a second thermal treatment is preferably performed betweenabout 600° C. and 800° C. by rapid thermal process to make, the phase ofthe salicide 310 change to another phase 320 with low resistance, asshown in FIG. 3F.

The foregoing description of the preferred embodiments of this inventionhas been presented for purposes of illustration and description. Obviousmodifications or variations are possible in light of the above teaching.The embodiments were chosen and described to provide the bestillustration of the principles of this invention and its practicalapplication to thereby enable those skilled in the art to utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. All such modifications andvariations are within the scope of the present invention as determinedby the appended claims when interpreted in accordance with the breadthto which they are fairly, legally, and equitably entitled.

What is claimed is:
 1. A method of forming a salicide, comprising:providing a silicon-based substrate comprising a source/drain and a gatewith a spacer on the side wall of the gate; forming a metal layer on thegate, the spacer, and the source/drain; performing a first thermaltreatment to react the portions of the metal in the metal layer with thesilicon in the gate and the source/drain to form a salicide; removingany unreacted metal and the spacer; introducing an ion containingsilicon into the source/drain; and performing a second thermaltreatment.
 2. The method as claimed in claim 1, wherein the material ofthe metal layer comprises Ti, Co, Ni, or Pt.
 3. The method as claimed inclaim 1, wherein the first thermal treatment is rapid thermal process(RTP).
 4. The method as claimed in claim 1, wherein the second thermaltreatment is rapid thermal process (RTP).
 5. The method as claimed inclaim 1, wherein the silicon ion is introduced by an ion implantation.6. The method as claimed in claim 1, wherein the metal layer is formedby sputtering.
 7. The method as claimed in claim 6, wherein thesputtering is processed by DC plasma.
 8. The method as claimed in claim1, wherein the unreacted metal and the spacer are removed by etching. 9.The method as claimed in claim 1, wherein the silicon-based substratefurther comprises a gate oxide below the gate.
 10. A method of forming asalicide, comprising: providing a silicon-based substrate comprising agate with a spacer on the side wall of the gate and a source/drain;forming a metal layer on the gate, the spacer, and the source/drain;performing a first rapid thermal process to react the portions of themetal in the metal layer with the silicon in the gate and thesource/drain to form a salicide; removing any unreacted metal and thespacer; performing a silicon ion implantation process; and performing asecond rapid thermal process.
 11. The method as claimed in claim 10,wherein the material of the metal layer comprises Ti, Co, Ni, or Pt. 12.The method as claimed in claim 10, wherein the metal layer is formed bysputtering.
 13. The method as claimed in claim 12, wherein thesputtering is processed by DC plasma.
 14. The method as claimed in claim10, wherein the unreacted metal and the spacer are removed by wetetching.
 15. The method as claimed in claim 10, wherein thesilicon-based substrate further comprising a gate oxide below the gate.